Complexation behaviours of acid-fractionated grain proteins with gum Arabic for beverage application: A comparative evaluation of Bambara groundnuts, pea and millet proteins
Student Durban University of Technology Durban, South Africa
Abstract: Protein- polysaccharide interactions are important in the structure formation in foods as well as in controlling physical and functional properties. This study investigated the complexation behaviours of acid – fractionated grain proteins with gum Arabic and evaluated their stability in model acidified beverage. Three grain proteins: bambara groundnuts ((Vigna subterranea), pea ((Pisum sativum) and millet (Pennisetum glaucum) were compared, and protein extractions were carried out at acidic medium ranging from pH 2 to 6. Proteins extracted using the tradition alkaline solubilisation (pH 8) method, were used as control. The extraction pH significantly affected the degree of complexation of proteins with gum Arabic. Protein – polysaccharide turbidity curves appeared skewed toward the acidic regions below pH 4.0 compared to homogenous and alkaline protein samples. Optimum pHs of complexations decreased as the protein extraction became more acidic. Protein fractions obtained at pH 6.0 showed better and stable optimum pH of complexation with gum arabic over a wide range of acidic pH region. The zeta potential profiles of acid fractionated proteins showed similar pH dependant patterns but with different isoelectric points. Differences in behaviours of proteins upon complexation could be linked to observed variation in composition, molecular weight distribution and complexity of protein. Although, some variations in particle size distribution were observed, protein-polysaccharide complexes obtained at pHopt appeared to be more stable when tested in a model acidified beverage. Complexes formed with Bambara and pea proteins appeared to produce more pronounced shift in optimum pH of complexation with gum Arabic and were more stable compared to those of millet. Findings suggest that the protein extraction pH at slightly acidic conditions (pH 6.0) could provide greater acid – stable structures upon complexing with polysaccharides.
